title: Structural insights into the polymorphism of amyloid-like fibrils formed by region 20-29 of amylin revealed by solid-state NMR and X-ray fiber diffraction.
abstract: Many unrelated proteins and peptides can assemble into amyloid or amyloid-like nanostructures, all of which share the cross-beta motif of repeat arrays of beta-strands hydrogen-bonded along the fibril axis. Yet, paradoxically, structurally polymorphic fibrils may derive from the same initial polypeptide sequence. Here, solid-state nuclear magnetic resonance (SSNMR) analysis of amyloid-like fibrils of the peptide hIAPP 20-29, corresponding to the region S (20)NNFGAILSS (29) of the human islet amyloid polypeptide amylin, reveals that the peptide assembles into two amyloid-like forms, (1) and (2), which have distinct structures at the molecular level. Rotational resonance SSNMR measurements of (13)C dipolar couplings between backbone F23 and I26 of hIAPP 20-29 fibrils are consistent with form (1) having parallel beta-strands and form (2) having antiparallel strands within the beta-sheet layers of the protofilament units. Seeding hIAPP 20-29 with structurally homogeneous fibrils from a 30-residue amylin fragment (hIAPP 8-37) produces morphologically homogeneous fibrils with similar NMR properties to form (1). A model for the architecture of the seeded fibrils is presented, based on the analysis of X-ray fiber diffraction data, combined with an extensive range of SSNMR constraints including chemical shifts, torsional angles, and interatomic distances. The model features a cross-beta spine comprising two beta-sheets with an interface defined by residues F23, A25, and L27, which form a hydrophobic zipper. We suggest that the energies of formation for fibril form containing antiparallel and parallel beta-strands are similar when both configurations can be stabilized by a core of hydrophobic contacts, which has implications for the relationship between amino acid sequence and amyloid polymorphism in general.
authors.affiliation: School of Biological Sciences, University of Liverpool, UK.
authors.forename: Jillian
authors.initials: J
authors.lastname: Madine
authors.forename: Edward
authors.initials: E
authors.lastname: Jack
authors.forename: Peter G
authors.initials: PG
authors.lastname: Stockley
authors.forename: Sheena E
authors.initials: SE
authors.lastname: Radford
authors.forename: Louise C
authors.initials: LC
authors.lastname: Serpell
authors.forename: David A
authors.initials: DA
authors.lastname: Middleton
mesh_terms: D000682:Amyloid / Q000737:chemistry* / Q000378:metabolism; D003460:Crystallization; D006801:Humans; D007515:Islets of Langerhans / Q000737:chemistry / Q000378:metabolism; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism; D017433:Protein Structure, Secondary; D014961:X-Ray Diffraction / Q000379:methods
chemical_list: D000682:Amyloid; D010446:Peptide Fragments; C117453:amylin (20-29); C109255:amylin (8-37)